feat(slice3): pure facet field-set + filter/count helper (§22.4a)

backend/tests/test_facets.py

@@ -0,0 +1,87 @@
+"""§22.4a SLICE-3 — pure facet field-set + filter/count (PUC-3).
+
+Per docs/design/2026-06-06-configurable-collection-metadata.md §5.1, §6.4.
+"""
+from app import facets
+
+
+PRIORITY = {"priority": {"type": "enum", "values": ["P0", "P1", "P2"]}}
+SCHEMA = {
+    "priority": {"type": "enum", "values": ["P0", "P1", "P2"]},
+    "tags": {"type": "tags"},
+    "owner": {"type": "text"},
+}
+
+
+def _e(slug, state="active", malformed=False, **meta):
+    return {"slug": slug, "state": state, "metadata_malformed": malformed, "meta": meta}
+
+
+def test_facet_fields_orders_declared_then_state_skips_text():
+    # enum + tags in declaration order, text skipped, state appended last.
+    assert facets.facet_fields(SCHEMA) == [
+        ("priority", "enum"), ("tags", "tags"), ("state", "enum")]
+
+
+def test_no_schema_yields_no_facets():
+    # INV-5: a collection with no fields has no facets (frontend keeps chips).
+    assert facets.facet_fields(None) == []
+    assert facets.facet_fields({}) == []
+
+
+def test_filter_and_count_basic_counts():
+    entries = [
+        _e("a", priority="P0", tags=["checkout"]),
+        _e("b", priority="P0", tags=["cart"]),
+        _e("c", priority="P1", tags=["checkout", "cart"]),
+    ]
+    items, fac = facets.filter_and_count(entries, SCHEMA, {})
+    assert {i["slug"] for i in items} == {"a", "b", "c"}
+    assert fac["priority"] == {"P0": 2, "P1": 1}
+    assert fac["tags"] == {"checkout": 2, "cart": 2}
+    assert fac["state"] == {"active": 3}
+
+
+def test_filter_compose_or_within_and_across():
+    entries = [
+        _e("a", priority="P0", tags=["checkout"]),   # P0 + checkout
+        _e("b", priority="P0", tags=["cart"]),        # P0, no checkout
+        _e("c", priority="P1", tags=["checkout"]),    # checkout, not P0
+    ]
+    # priority=P0 AND tags=checkout → only "a".
+    items, _ = facets.filter_and_count(
+        entries, SCHEMA, {"priority": {"P0"}, "tags": {"checkout"}})
+    assert {i["slug"] for i in items} == {"a"}
+
+
+def test_drilldown_counts_exclude_own_field_selection():
+    entries = [
+        _e("a", priority="P0"),
+        _e("b", priority="P1"),
+        _e("c", priority="P1"),
+    ]
+    # With P0 selected, the priority facet still counts P1 over the set that
+    # ignores priority's own selection — so P1 stays switchable.
+    _, fac = facets.filter_and_count(entries, SCHEMA, {"priority": {"P0"}})
+    assert fac["priority"] == {"P0": 1, "P1": 2}
+
+
+def test_malformed_toggle_narrows_items_and_counts():
+    entries = [
+        _e("a", state="active", malformed=True, priority="P9"),
+        _e("b", state="active", malformed=False, priority="P0"),
+    ]
+    items, fac = facets.filter_and_count(entries, SCHEMA, {}, only_malformed=True)
+    assert {i["slug"] for i in items} == {"a"}
+    assert fac["priority"] == {"P9": 1}
+
+
+def test_missing_value_contributes_no_facet_value():
+    entries = [_e("a", priority="P0"), _e("b")]  # b has no priority
+    _, fac = facets.filter_and_count(entries, SCHEMA, {})
+    assert fac["priority"] == {"P0": 1}
+
+
+def test_allowed_filter_keys():
+    assert facets.allowed_filter_keys(PRIORITY) == {"priority", "state",
+                                                    "unreviewed", "malformed"}